1. The Field of the Invention
The present invention is related to biocompatible implants for treating defects in living organisms, such as bone defects and tooth extraction wounds. More specifically, the present invention relates to moldable biocompatible implants.
2. Related Technology
The importance of bone replacement materials, in particular in the areas of orthopedics, traumatology, cranial, dental and facial surgery, and orthodontics continues to increase. Significant areas of application for bone implants include, for example, the closing of large bone defects associated with comminuted fractures as well as the attachment of small bone fragments, the filling of bone defects resulting from bone cysts and after removal of bone tumors, the filling of voids caused by chronic osteomyelitis, applications associated with material loss on alveolis and jaw bones and the use as a carrier material, for example, for antibiotics, cytostatic, and osteogenic materials.
In most cases, bone defects can be treated by the insertion of bone augmentation materials. Healing is promoted if the implants closely contact the surrounding bone walls. Thus, it is advantageous to be able to form a bone implant in a particular shape. For instance, if a tooth is extracted, the bone implant used to fill the void preferably nearly replicates the tooth root. Improperly shaped bone implants can lead to problems such as soft tissue ingrowth and poor adhesion between the implant and existing bone. In addition, improper shape can lead to complications or patient discomfort.
Properly shaping a bone implant is often very challenging. In some cases the repair site is deep within the body and covered by soft tissue and body fluids. In other cases, such as with a tooth extraction, the root of the extracted tooth can be used to make a mold. However, even when repairing a tooth extraction wound, there are times when the root is broken into pieces and not available for molding. In other situations, the bone implant must be molded after it has been placed in the injury site. Most existing bone implant materials, however, require steps, such as heating, that prevent forming the implant in-vivo.
One type of existing implant uses calcium phosphate or bioglass granules to fill and treat bone defects. These granular-type implants are biodegradable and osteoconductive. While existing granular bone implants can promote bone tissue in-growth, the formation and retention of these implants can be complex. In some cases, a membrane is required to maintain the granules at the implantation site.
Another type of implant system uses injectable materials such as a polymer solution or a dispersion of microparticles. The injectable systems improve handling and moldability. However, injectable systems are typically non-biodegradable and prevent new bone formation throughout the implant (i.e. they have low osteoconduction). For example a known injectable material such as polymethylmethacrylate (PMMA) is non-biodegradable and inhibits natural bone from forming in the bone defect. Calcium phosphate cements can be biodegradable, but often lead to the formation of dense or solid or may contain small closed pores implants that inhibit osteoconduction.
One recent bone implant that improves upon the injectable polymer implants uses a solid polymeric material that is soaked in an organic solvent such as N-methyl-2-pyrrolidone (NMP) to soften the implant. The implant can then be molded to a desired shape in-situ. This implant, however, is also solid and non-porous or may contain small pores. The natural bone surrounding the implant cannot integrate into this implant nor replace it with regenerative bone tissue, unless the implant is degraded. Unlike an osteoinductive and/or osteoconductive implant, these implants have limited use for restoring the wound or defect to a more natural condition (i.e., they fill rather than heal the defect).
In another attempt to improve bone implants, a defect analog or mold is made from a piece of extracted bone, such as an extracted tooth root. The mold can then be used to make a porous and biodegradable replica. One disadvantage of using a defect analog is that it requires the integrity of a tooth root or other piece of bone to make the mold. In addition, the implant manufacturing process often requires a small heating device or a CO2 autoclave, thus increasing the expense and complexity of the process. Even where shaping the implant in a mold is desired, there is a need to simplify the process for shaping regenerative bone implants such that the implants can be shaped in a more timely fashion.
Therefore, what is needed is a biodegradable implant that can be easily and quickly shaped in-situ or ex-situ into a desired form and that can promote the in-growth and regeneration of bone tissue.